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stream.scm
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stream.scm
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(define (stream-car stream)
(car stream))
(define (stream-cdr stream)
(force (cdr stream)))
(define (stream-ref s n)
(if (= n 0)
(stream-car s)
(stream-ref (stream-cdr s) (- n 1))))
(define (stream-map proc . argstreams)
(if (stream-null? (car argstreams))
the-empty-stream
(cons-stream
(apply proc (map stream-car argstreams))
(apply stream-map
(cons proc (map stream-cdr argstreams))))))
(define (stream-for-each proc s)
(if (stream-null? s)
'done
(begin
(proc (stream-car s))
(stream-for-each proc (stream-cdr s)))))
(define (display-stream s)
(stream-for-each display-line s))
(define (display-stream-upto s count)
(cond ((or (stream-null? s)
(zero? count))
'done)
((> count 0)
(begin
(display-line (stream-car s))
(display-stream-upto
(stream-cdr s)
(- count 1))))
(else (display-stream-upto
(stream-cdr s)
(- count 1)))))
(define (display-line x)
(newline)
(display x))
(define (stream-enumerate-interval low high)
(if (> low high)
the-empty-stream
(cons-stream low (stream-enumerate-interval
(+ low 1)
high))))
(define (stream-filter pred stream)
(cond ((stream-null? stream) the-empty-stream)
((pred (stream-car stream))
(cons-stream
(stream-car stream)
(stream-filter
pred
(stream-cdr stream))))
(else (stream-filter pred (stream-cdr stream)))))
(define (show x)
(display-line x)
x)
(define (add-streams s1 s2)
(stream-map + s1 s2))
(define (mul-streams s1 s2)
(stream-map * s1 s2))
(define (scale s factor)
(stream-map (lambda (item) (* factor item)) s))